Does Greywater with Tallow Based Soap in it kill plants?

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Deb Walker

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A "greenthumb" friend told me watering her plants with greywater that has tallow based soap in it ends up killing her plants. Does anyone have any info on this? It seems strange to me that this would be the case but would rather find out beforehand.
We are on tank water and haven't had rain for such a long time and I want to use any water I can save for my plants.
Sometimes there are other factors people overlook and form inaccurate conclusions.
Coming from the land of the persistent Long White Cloud (NZ) to the land of Regular Drought (Aussie) in more recent years its not something I have had to think about and I have put a lot more money into my garden and want to do the best for it.

Maybe plants have gone vegan :).
 

earlene

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I don't believe that simply having sodium tallowate as one of the ingredients is going to kill plants. If your friend is having that happen, perhaps she uses too much soap in her laundry or where ever her greywater is coming from. Perhaps she is over-watering and drowning them. I really don't believe the tallowate itself is the cause. There may be something else at play here; some other factor. Or maybe it's the specific types of plants that she has and perhaps she does not use a greywater cleaning system to remove certain chemicals that can build up in the soil over time from greywater.

My brother & SIL have been using greywater from their baths, dishwasher & washing machine for a couple of decades and none of their plants die from it. They have numerous fruit trees, an abundance of vegetables, and some ornamentals and flowers. I believe they use a commercial dish washing soap, but SIL also makes liquid laundry soap using whatever kind of bar soap she has on hand. When they buy commercial soap, they often buy brands that include sodium tallowate on the ingredient list. Occassionally I send her some coconut oil soap to use in her laundry soap but mostly she used commercial soap she can buy in the supermarkets.

But there are other possibilities in greywater that might be worth looking into. Here are a couple of links with more information:

https://homeguides.sfgate.com/gray-water-vs-tap-water-plants-71360.html
https://www.gardenmyths.com/gray-water-safe-garden/

I don't know what cleaning methods my brother installed for their greywater usage. He is an engineer, so I do believe he did install at least a filtering system of some sort, but I don't recall what he said he did because we haven't talked about their system for a very long time.

But they also have chickens and that adds to the fertilizing components and they also compost, so it's not just the water contributing to the soil.
 

lsg

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The old timers here, used their dish washing water to water outside plants. Of course, the soap they used was old time lye soap.
 

Martha

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Is it possible that your friend’s grey water is warm/hot? That could kill plants for sure.
 

geniash

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I use greywater all the time to water the plants. There is a catch though - I use special laundry detergent called Oasis - it is bioavailable, meaning it breaks down to plant available nutrients immediately or shortly after the laundry.
Having said this, I also used water from laundry with the soap I made to water the plants. None died. I suspect your friend might have had lye heavy soap that killed the plants OR she used too much water to water them. Soapy water has pH on a slightly alkaline side while most plants prefer slightly acidic.
 

Becky1024

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I use greywater all the time to water the plants. There is a catch though - I use special laundry detergent called Oasis - it is bioavailable, meaning it breaks down to plant available nutrients immediately or shortly after the laundry.
Having said this, I also used water from laundry with the soap I made to water the plants. None died. I suspect your friend might have had lye heavy soap that killed the plants OR she used too much water to water them. Soapy water has pH on a slightly alkaline side while most plants prefer slightly acidic.
I'm thinking it may be the pH too. If it's alkaline your friend may want to bring the pH down by adding a little acid.
 

Deb Walker

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Thanks for the comments. Like I said it did seem strange to me.
I had also forgotten that people make "white oil" for aphid spray and use natural soap as the surfactant/emulsifier.
Happy soaping
 

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